Production of adhesives and adhesive bases from synthetic rubber latex by causing phase inversion with a protective colloid and adding organic solvent



United States Patent O PRODUCTION OF ADHESIVES AND ADHESIVE BASES FROMSYNTHETIC RUBBER LATEX BY CAUSING PHASE INVERSION WITH A PRO- TECTIVECOLLOID AW ADDING ORGANIC SOLVENT Charles F. Fryling, Pittsburgh, Pa.,assiguor to Phillips Petroleum Company, a corporation oi Delaware NoDrawing. Application July 18, 1952, Serial No. 299,743

8 Claims. (Cl. 26(i33.6)

This invention relates to methods of preparing adhesive compositions. Inone of its more specific aspects the invention relates to the productionof an adhesive base from synthetic rubber latex. In another aspect thisinvention pertains to the production of adhesive composi tions from highsolids synthetic rubber latices.

It is known in the art that synthetic rubber can be dissolved in organicsolvents to produce adhesive bases which are employed in the preparationof adhesives or adhesive compositions. However, the problem of preparingadhesive bases involves certain difficulties and inconveniences. If thesynthetic rubber is prepared by emulsion polymerization, as is mostfrequently the case, a latex is obtained. When it is desired to preparea solution of the rubber in an organic solvent, one method is to recoverthe rubber from the latex by suitable coagulation, separation, anddrying steps and then treat it with a solvent. When rubber is obtainedfrom the latex in the form of a dry crumb, it is not readily soluble inmost solvents and considerable time is consumed in preparing solutionsof the desired concentration, for example, in some instances the rubberis broken up into small particles to aid solution. Attempts have beenmade to prepare synthetic rubber solutions directly from the latex butin such cases it is generally necessary to use solvent extraction toaccomplish solution of the rubber. At best considerable time is consumedin an operation of this type.

I have now discovered a very rapid and convenient method for preparingadhesive bases directly from the latex. By adhesive base I mean asolution of rubber in a rubber solvent which is made into an adhesive bythe addition of modifying and other agents, heating, etc. The methodsemployed in accordance with this invention are particularly suitable tothe production of adhesive bases because they are applicable to naturalrubber latex, synthetic rubber latices and also to high solids syntheticrubber latex. In accordance with an embodiment of the instant inventionan adhesive base is provided by incorporating into liquid rubber latex aprotective colloid in an amount sufiicient to cause phase inversion andsubsequently dissolving rubber polymer dispersed in the resultinginverted emulsion with a water immiscible rubber solvent. Phaseinversion means the breaking of the continuity of the aqueous phase inthe latex so that what was an oil-in-water emulsion becomes awater-in-oil emulsion.

The protective colloids are substances which behave as hydrophiliccolloids when they are dispersed in water. Synthetic rubber latex is anemulsion in which water is present as a continuous phase. It can bediluted with water to give a latex having any solids content desired.Treatment with a protective colloid effects a change in the latex toproduce an inverted emulsion in which water is no longer present as acontinuous phase. This so-called inverted emulsion cannot be dilutedwith water to give a smooth latex as before. Instead the solid materialremains inthe form of lumps or chunks in the water added. However, uponthe addition of an organic solvent, the rubber dissolves immediately. Ifthe solution is allowed to stand, any water which was present in thelatex will separate as an aqueous phase in which is contained theemulsifying agent and any salts employed in the polymerization recipe,and the protective colloid. The aqueous phase can be removed thusleaving a solu tion of synthetic rubber in the organic solvent.

A desirable method of preparing adhesive bases in accordance with thisinvention is to add a protective colloid in the form of a dry powder.For example, a protective colloid in the form of a dry powder is addedto the synthetic rubber latex, and the materials intimately mixed by anysuitable means. Mixing need be continued only until phase inversionoccurs, that is, until the material is homogeneous. The time required isgoverned by the viscosity of the latex, type of agitation, and the like,but will generally be in the range from 2 to 30 minutes. The solvent isthen added and the mixture stirred to effect solution. It is notnecessary to heat the mixture as the rubber dissolves readily at roomtemperature. It is frequently considered advisable to allow the mixtureto stand in order that any water present will separate but this stepwill depend upon the amount of Water present and the ultimate use of thesynthetic rubber solution. It is very convenient and frequentlypreferred to use a high solids paste latex such as is described inapplication Serial No. 253,342 of Wicklatz and Kennedy filed October 26,1951. Although the rubber base per se can be used for bonding rubbersheet or as an additive in household cements, rubber adhesivesthemselves require formulation. Their formulation is generally complexbut it is well known to the rubber technologist. For exampleaccelerators, anti-oxidants, vulcanizing agents, tackifiers and/orplasticizers will be added. In addition the base may be further modifieddepending on the specific application desired.

The amount of protective colloid employed must be sufficient to causephase inversion, conveniently indicated by the addition of Water. Ifphase inversion has not taken place a smooth latex will form upon theaddition of water; if phase inversion has taken place a smooth latexwill not form, but instead the polymer will separate due to theformation of coagulum. For the most part the minimum amount ofprotective colloid can be determined from the quantity of soap presentin the recipe by which the latex was made. For example, if 5 parts byweight of soap were used in the recipe, which is the quantity frequentlyused in polymerization systems based on parts by weight of monomericmaterial, no less than 0.5 part by weight of protective colloid need beused, in other words a minimum amount of protective colloid necessary is0.1 part per 1 part of soap by weight. The upper limit is determined bypractical considerations. When the amount of protective colloid is basedupon the soap in the recipe it is normally not necessary, regardless ofthe quantity of soap employed in a recipe, to use more than 40 parts byweight of the protective colloid per 100 parts by weight of rubbersolids. A desirable range is, therefore, 0.1 part to 8 parts by weightof the protective colloid per 1 part of soap. In many instances, such asin the case of natural rubber latex, the amount of protective colloidemployed will be more conveniently based upon rubber solids content. Interms of rubber solids content the amount of protective colloid will bein the range of 0.5 to 35 parts by Weight of the agent per 100 parts byweight of rubber solids. Hydrophilic protective colloids are, asimplied, materials which are solvated by water but not by organicsolvents. Examples are albumin, casein, gelatin, glue, Irish moss, watersoluble cellulose esters, gum tragacanth, agar, gum guai-ac, dextrin,soluble starches and "the like.

The solvents employed in the practice of this invention to dissolve therubber after inversion has occurred are normally water immiscibleorganic rubber solvents. Solvents which are generally preferred arehydrocarbons, particularly aromatic hydrocarbons such as benzene,toluene, xylene, and the like but aliphatic hydrocarbon solvents such aspetroleum ether, kerosene, hexane, cyclohexane, etc. are alsoapplicable. Other solvents which can be used are halogenated aliphaticcompounds such as carbon tetrachloride, chloroform, methylene chloride,etc. Nitroparailins, such as nitrornethane and nitroethane, and variousothers can also be used. The amount of solvent will vary depending uponthe concentration of the rubber solution desired. Rubber solutionsvarying in concentration from 0.5 to 50 per cent by Weight or higher aredesirable, the upper limit being governed by the ability of the solventto dissolve the rubber.

The novel method of preparing adhesive bases can be more readilyunderstood by reference to the following examples. It is understood, ofcourse, that the examples are illustrative and that the invention is notto be limited thereby.

Example 1 A latex paste containing 62 per cent solids was prepared bythe copolymerization of butadiene with styrene at 5 C. in accordancewith the following recipe:

Parts by weight Butadiene 70 Styrene Water 30 Potassium oleate 5Mercaptan blend 1 0.30 FeSO.7HzO 0.20 KaPzOr 0.27Tert-butylisopropylbenzene hydroperoxide 0.26

1A blend of tertiary C12, C14, and C16 aliphatic mercaptans in a ratioof 3 l 1 parts by weight.

When carrying out the polymerization, potassium oleate was formed insitu by the following procedure. Water, oleic acid, styrene, mercaptanblend, and butadiene were charged to the reactor and agitated until thefatty acid and mercaptan were dissolved in the monomer phase. (Asuthcient amount of water was withheld for preparation of the KOH andactivator solutions.) Potassium hydroxide was then introduced in anamount required to give 95 per cent neutralization of the oleic acid (pHof the system was approximately 10.3). The mixture was agitated forabout 30 minutes during which time the temperature was adjusted to 5 C.The hydroperoxide, dissolved in about 20 per cent of the styrene whichwas withheld for this purpose, was introduced and then the ferrouspyrophosphate activator solution. The activator solution was previouslyprepared by dissolving the ingredients separately in water, pouring theferrous sulfate into the pyrophosphate, and heating the mixture at 60 C.for minutes. A latex paste containing 62 per cent solids (79 per centconversion) was obtained after a reaction period of 48 hours. The runwas not shortstopped and the unreacted monomers were not removed. Thesolids content was determined by withdrawing a sample using the syringetechnique. The sample was weighed (syringe containing sample weighed,sample discharged, and syringe weighed again), dried on a hot plate, andthe residue weighed. From a 1.2 gram sample, 0.74 gram solids wasobtained. Calculation showed the latex to have a solids content of 62per cent. The per cent conversion was determined in the followingmanner:

Grams Recipe weight 136 Solids (soap, etc.) in recipe 6 8d.36=7 8.3%conversion A sample of the latex paste prepared as described above wasmixed with 20 per cent of its weight of powdered albumin until ahomogeneous material was obtained. Based on a 62 per cent solids latex,this represents 32 parts albumin per parts rubber solids. Approximatelyfive minutes was required. Toluene, approximately four volumes pervolume of latex, was added and the rubber dissolved immediately. Afterallowing the mixture to stand, an aqueous layer separated and wasremoved leaving a clear solution of rubber in toluene.

Example 2 One sample of the latex paste prepared in Example 1 wasdiluted with Water. A smooth latex formed immediately thus demonstratingthat the latex could be diluted with water to any solids contentdesired. To another sample of the latex toluene was added and themixture agitated. After 15 minutes there was no apparent evidence ofsolution of the rubber in the organic solvent. A third sample of thelatex was masticated with albumin and this mixture divided into twoparts. Water was added to one part. A smooth latex did not form as wasthe case with the sample containing no albumin. Toluene was added to thesecond portion and the rubber dissolved readily to form a clearsolution. These results indicate that phase inversion had taken placeupon treatment of the latex with albumin.

The above examples clearly illustrate a desirable method of preparingadhesive bases. prepared must, of course then be treated by any of theavailable methods to produce adhesives having desired properties.However these methods are well known to those skilled in the art, e. g.,the base can be modified by heat treatment. by the addition of modifyingagents and other substances to improve tack such asmercaptobenzothiazole, or vegetable or mineral oils or resins such asphenol or resorcinol resins to produce a desired adhesive. Obviouslymany modifications or variations of the invention as hereinbefore setforth may be made without departing from the spirit and the scopethereof. Thus besides rubber copolymers of butadiene and styrene theinvention is applicable to elastic polymers of butadiene, and elasticcopolymers of butadiene, isoprene and other simple dienes with eachother and with vinyl compounds of many types, for example polymers andcopolymers of piperylene and copolymers of butadiene with chlorostyrenesor acrylonitrile.

I claim:

1. A process for the production of an adhesive base which comprisesincorporating into a high solids content rubber latex a SdfilClfilltamount of protective colloid to cause phase inversion of the latex,conveniently indicated by separation of the polymer as coagulum uponaddition of water to the latex; subsequently adding to the invertedemulsion a sufficient amount of a water-immisicible rubber solvent todissolve the rubber content thereof, and by phase separation recoveringthe rubber-in-solvent solution from the Water originally present in thelatex.

2. A process for the production of an adhesive base which comprisesmixing a high solids content synthetic rubber latex, prepared from arecipe using soap, with a protective colloid so as to cause phaseinversion of the latex, conveniently indicated by separation of thepolymer as coagulum upon addition of water to the latex, at least 0.1part by weight of the protective colloid being added per 1 part byweight of soap used in the latex recipe; dissolving the rubber polymercontent of the resulting inverted emulsion with a water insoluble rubbersolvent, and by phase separation recovering the solution of rubber fromthe water initially present in the latex.

3. Process of claim 2 wherein 0.1 to 8 parts by weight of the protectivecolloid are added to 1 part by weight of the soap used in the latexrecipe.

4. A process for the production of an adhesive base which comprisesincorporating into a high solids content natural rubber latex asufiicient amount of a protective The adhesive bases so I colloid tocause phase inversion, conveniently indicated by separation of thepolymers as coagulum upon addition of water to the latex, the amount ofprotective colloid added being in the range of 0.5 to 35 parts by weightper 100 parts by weight of rubber solids; dissolving the latter bymixing the resulting inverted emulsion with a water-insoluble rubbersolvent, and by phase separation recovering the rubber solventcontaining dissolved rubber from the water originally present as acontinuous phase in the latex.

5. A process which comprises incorporating into a high solids contentliquid rubber latex a protective colloid in an amount sufiicient tocause phase inversion, conveniently indicated by separation of therubber as coagulum upon addition of water to the latex; subsequentlydissolving the rubber content by mixing the resulting inverted emulsionwith a water-immiscible rubber solvent; by phase separation recoveringthe solvent containing dissolved rubber from the water initially presentin the latex as a continuous phase, adding sutficientmercaptobenzothiazole to the separated solvent to improve the tackthereof, and diluting the resultant product as desired to produce anadhesive composition.

6. A process for the production of an adhesive base which comprises;into a synthetic rubber latex, prepared from a recipe using soap, andcontaining from 60 per cent to 90 per cent solids incorporating powderedalbumin in a ratio of 0.1 to 8 parts by weight of powdered albumin to 1part by weight of soap used in the latex recipe, sufficient to causephase inversion, subsequently dissolving said rubber by mixing theresulting inverted emulsion with toluene and recovering the toluenecontaining dissolved rubber polymer from water initially present in thelatex as a continuous phase.

7. A process for the production of an adhesive base which comprisesintimately mixing 32 parts of powdered albumin by weight based 011 100parts of dry rubber solids and a synthetic rubber latex containing 62per cent solids formed by the emulsion polymerization of a major amountof butadiene with a minor amount of styrene in an iron pyrophosphatesystem with potassium oleate as the emulsifier, after phase inversionoccurs adding 4 volumes of toluene per volume of latex to dissolve therubber solids and by phase separation recovering the toluene containingdissolved rubber polymer from water initially present in the latex as acontinuous phase.

8. A process for the production of an adhesive base which comprisesintimately mixing 32 parts of powdered albumin by weight based on 100parts of dry rubber solids and a synthetic rubber latex containing 62per cent solids formed by the emulsion polymerization of parts by weightof butadiene with 30 parts by weight of styrene at 5 C. in an ironpyrophosphate system with potassium oleate as the emulsifier, afterphase inversion occurs adding 4 volumes of toluene per volume of latexto dissolve the rubber solids and by phase separation recovering thetoluene containing dissolved rubber polymer from water initially presentin the latex as a continuous phase.

References Cited in the file of this patent UNITED STATES PATENTS2,419,060 Edwards Apr. 15, 1947 2,495,135 Rodman Jan. 17, 1950 FOREIGNPATENTS 205,487 Great Britain Oct. 30, 1924

1. A PROCESS FOR THE PRODUCTION OF AN ADHESIVE BASE WHICH COMPRISESINCORPORATING INTO A HIGH SOLIDS CONTENT RUBBER LATER A SUFFICIENTAMOUNT OF PROTECTIVE COLLOID TO CAUSE PHASE INVERSION OF THE LATEX,CONVENIENTLY INDICATED BY SEPARATION OF THE POLYMER AS COAGULUM UPONADDITION OF WATER TO THE LATEX; SUBSEQUENTLY ADDING TO THE INVERTEDEMULSION A SUFFICIENT AMOUNT OF A WATER-IMMISICIBLE RUBBER SOLVENT TODISSOLVE THE RUBBER CONTENT THEREOF, AND BY PHASE SEPARATION RECOVERINGTHE RUBBER-IN-SOLVENT SOLUTION FROM THE WATER ORIGINALLY PRESENT IN THELATEX.